System for monitoring temperature inside electric machines

ABSTRACT

The electric machine comprises at least one winding made of a material having a temperature dependent resistance. The temperature of the winding is monitored using the resistance therein. Temperatures or resistances indicative of a fault can be sensed, and corrective action taken, without the need for dedicated temperature sensors.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

The present application is a divisional of U.S. patent application SerNo. 11/419,239, filed May 19, 2006, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The invention relates to temperature monitoring inside electricmachines.

BACKGROUND

In the unlikely event of a turn to turn short-circuit or otherelectrical fault inside an electric machine such as a motor orgenerator, the temperature at the faulted winding can becomesignificantly elevated and thereby pose a risk to the continuedoperation of the machine. However, no other symptoms may be evidentinitially, until the insulation of the winding deteriorates to asignificant level, after which a more serious thermal condition mayresult. Providing temperature sensors to sense a high temperature withina faulted winding can detect a fault, however, such arrangement addscomplexity to the electric machine. Room for improvement exists.

SUMMARY

In one aspect, the present invention provides a method for monitoringtemperature of at least one winding of an electric machine, the windinghaving a temperature dependant resistance, the method comprising:determining a resistance of the winding while in operation; anddetermining a winding temperature of the winding using the resistancetherein.

In another aspect, the invention provides a system for monitoringtemperature of at least one winding of an electric machine, each windinghaving an electrical resistance which changes with temperature, thesystem comprising: a monitor adapted to determine a value indicative ofthe instantaneous resistance in at least a portion of the at least onewinding; and a processor adapted to calculate an instantaneoustemperature based on the resistance, and determine the presence of afault condition based on the temperature.

In a further aspect, there is provided an electric generator systemcomprising a generator having a permanent magnet rotor and a stator, thestator having at least one output winding connected to a generator loadand at least one control winding, the windings disposed in stator slots,the stator defining a first magnetic circuit passing through the statoraround a portion of the at least one output winding, the stator defininga second magnetic circuit passing through the stator around anotherportion of the at least one output winding and a portion of the at leastcontrol winding, the first and second magnetic circuits remote from oneanother, the at least one control winding having an electricalresistance which varies with temperature; a current source connected tothe at least one control winding adapted to provide variable DC currentthereto, the source and the at least one control winding providing acontrol circuit; and a fault detection apparatus connected to thecontrol circuit, the fault detection apparatus adapted to determine anelectrical resistance of the at least one control winding and detect afault therefrom.

BRIEF DESCRIPTION OF THE FIGURES

Reference will now be made to the accompanying figures, in which:

FIGS. 1a and 1b are a schematic cross-sectional views of examples of anelectric machine suitable for use with the present invention; and

FIG. 2 is a block diagram showing an example of a system for monitoringthe temperature of an electric machine winding.

DETAILED DESCRIPTION

FIG. 1a shows an example of an electric machine 10 of the general typedescribed in applicant's U.S. Pat. No. 6,965,183, while FIG. 1b shows anexample of an electric machine of the general type described inapplicant's co-pending application Ser. No. 10/996,411, bothincorporated herein by reference. In both cases, the machine 10 can beused as a motor and/or a generator, and includes a rotor 12 (a permanentmagnet rotor is shown in the figures) and a stator 16 having a pluralityof primary windings 18 and secondary windings 20. The primary windings18 generate output power in response to rotor rotation (generator) orcreate a rotating electromagnetic field to cause rotor rotation (motor).The secondary windings 20 are used to control the operation of theelectric machine 10 through affecting primary windings 18, as describedin the incorporated references. A rotor magnetic circuit 22 and asecondary magnetic circuit 24 are defined in the stator 16 for directingmagnetic flux within the machine 10. Secondary windings 20 arepreferably aluminium, copper or other material (whether pure, alloy orcomposite, etc.) in which material temperature affects the material'selectrical resistivity.

FIG. 2 schematically illustrates an example of a system 30 formonitoring the temperature of one or more secondary windings 20 (threewindings connected in series are shown in this example), while machine10 is in operation without the need for dedicated temperature sensors orthermocouples. The system 30 comprises a monitoring device 32 connectedin series with the windings of interest, in this case secondary windings20. If there is more than one set of target windings in the machine 10,more than one monitoring unit 32 per machine may be provided.

The secondary windings 20 of machine 10 actually comprise a plurality ofwindings that are connected in series, and are also connected to avoltage source, in this case preferably a variable DC source 25. Themonitoring device 32 is adapted to determine parameters used todetermine winding resistivity, such as voltage and current in thesecondary windings 20.

Once obtained, the parameters are sent to a processor 34, which may ormay not be integrated within the monitoring device 32, as desired. Theprocessor 34 calculates the instantaneous winding resistance based onthe provided parameters. In this case, the voltage and the current datais used to obtain the resistance simply using Ohm's law (i.e. V=IR).Other parameters and other techniques may be used. Whatever thetechnique used, by monitoring relevant operational parameters of thetarget winding, such as voltage and current flow through the controlwindings 20, one can monitor resistance. When the target windings aremade of a temperature dependent material, for instance aluminium orcopper, the temperature of the windings may be determined from theresistance. This could be done, for instance, using a suitable algorithmin the processor 34, or by using a look-up table stored in a memory 36,or in any other suitable manner.

In use, in the event of a short-circuit causing the local temperature inthe faulty winding to increase, thereby changing its resistance, theaverage resistance of the winding or windings will correspondinglyincrease, and this will be detected by the system. Comparison of aresistance change against a selected threshold will indicate theexistence of a fault or other condition requiring attention. Upondetection of a resistance change indicative of a fault condition, asuitable corrective action can be taken, such as to notify a machineoperator, to notify a machine controller for automatic machine shutdownor other fault mitigation, and/or to notify a machine maintenancemonitoring system for logging an appropriate maintenance action, to namejust a few. As well, gradual changes in resistance may be monitored overtime for an overall indication of a health trend of the machine, andparameters indicating that a presently operational machine may soonbecome subject to a fault can be sensed, the fault predicted and anappropriate corrective action taken in advance of any occurrence of thefault.

As can be appreciated, the present system and method can be used tomonitor the temperature inside the electric machine without a need ofdedicated temperature sensors therein. The system can also be used as anadditional monitoring system, if required, when dedicated temperaturesensors are provided.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that other changes may also be made to theembodiments described without departing from the scope of the inventiondisclosed as defined by the appended claims. For instance, the presentinvention is not limited for use with the machine as shown in FIGS. 1and 2, and it may be used with other suitable machine designs as well.The type and nature of the windings monitored may be any suitable, andthe material of which the target windings are made may likewise be anysuitable. The monitoring of the winding's parameters may be done in anysuitable manner, and any suitable technique may be used to determine thewinding's resistance. Other changes from the described embodiment may beapparent to the skilled reader, and are not meant to be excluded fromthe scope of the appended claims merely because all possible variantsand changes have not been exhaustively described.

What is claimed is:
 1. An electric generator system comprising: agenerator having a permanent magnet rotor and a stator, the statorhaving a plurality of primary windings configured to generate outputpower in response to rotation of the rotor when connected to a generatorload and a plurality of series-connected secondary windings configuredto control the operation of the generator through affecting theplurality of primary windings, the plurality of series-connectedsecondary windings having an electrical resistance which varies withtemperature; a current source connected in series with the plurality ofseries-connected secondary windings and adapted to provide a variable DCcontrol current to the plurality of series-connected secondary windingsto control the operation of the generator by affecting the plurality ofprimary windings, the current source and the plurality ofseries-connected secondary windings providing a control circuit; and afault detection apparatus connected to the control circuit, the faultdetection apparatus adapted to determine an electrical resistance of theplurality of series-connected secondary windings as an indication oftemperature of the plurality of series-connected secondary windingsbased on the variable DC control current provided to the plurality ofseries-connected secondary windings and detect a fault from thedetermined electrical resistance.
 2. The system of claim 1 wherein theresistance is an average resistance across the plurality ofseries-connected secondary windings.
 3. The system of claim 1 whereinthe fault detection apparatus is connected in series with the pluralityof series-connected secondary windings.
 4. The system of claim 3 whereinthe fault detection apparatus is adapted to determine a voltage dropacross the plurality of series-connected secondary windings and thecurrent passing through the plurality of series-connected secondarywindings.